Electric power is supplied to homes and industries through the electrical power system. The electrical power system is an interconnected network that includes power generating plants that produce electrical power, high-voltage transmission lines that carry power from distant sources to demand centers, and distribution lines that supply individual users with electricity. The transmission and distribution lines of the power system, or portions thereof, are often referred to as the grid, or power grid.
For electrical devices receiving electricity from the power system to function properly, the voltage of the electricity supplied by the power system must be of high quality. Voltage fluctuations, which are rapid and noticeable changes in the root mean square (rms) voltage level of the electricity supplied by the power system, can degrade the power quality and affect the performance of electrical devices. For instance, the effect of such voltage fluctuations can be perceived in visible changes of the brightness of a lamp, causing the light level of the lamp to fluctuate, or flicker. Thus, the term “flicker” or “voltage flicker” is often used to refer to such voltage fluctuations. Voltage flicker can be caused by a fluctuating electric load when various equipment or facilities change the load current on, for instance, the distribution level of the grid of the power system.
Regulators establish guidelines, or limits, for the maximum acceptable levels of voltage flicker that can be tolerated by customer electronic devices receiving electricity through the power system. One such guideline is shown in FIG. 1, which is a voltage flicker tolerance curve from the IEEE Standard 141-1993/IEEE Standard 519-1992, known as the “GE Flicker Curve.” The GE Flicker Curve shows the point at which, for a given size and frequency of a voltage fluctuation (referred to as a dip), a typical person begins to perceive visible flicker in the brightness of a lamp, and the point at which a typical person would become irritated by such visible flicker.
When new facilities are installed on the electrical power system, or other changes that may affect the voltage levels are made to the electrical power system, such changes are evaluated for their impact on voltage flicker. The voltage flicker caused by such new facility installations or other changes typically must be within the acceptable levels set by regulators, for instance under the levels determined by the GE Flicker Curve. If the voltage flicker exceeds the flicker limits, costly equipment is often required to be added to the facility to bring the voltage flicker within acceptable levels.